1. Field of the Invention
The present invention relates to methods of and devices for introducing inspection equipment into piping systems. More particularly, the present invention relates to controlling the movement of inspection equipment within piping systems by using relative hydrostatic pressure.
2. Discussion of Background
In fluid piping systems, it is well known to pass various types of cleaning devices, typically referred to as "pigs", through the piping systems along with the flowing fluid. This cleaning process is especially useful in gas pipelines to remove the build-up of liquid deposits caused by water and hydrocarbon vapors condensing in the piping system.
In addition to cleaning pigs, other devices are passed through piping systems for cleaning purposes. Cup pigs, spheres, line scrapers, "bullets" and the like are forced through the pipelines to clean the interior of the piping system. Also, numerous devices for launching the pigs into the piping system are described in the prior art. For example, in U.S. Pat. No. 3,266,076, Surber discloses a pipeline cleaning system having a pig launcher and conduits connected to the pipeline upstream of the launcher that forms a manifold for introducing the pigs into the pipeline. Launching of the pigs is caused by introducing gas into one of the conduits, which causes the launching of the immediately-downstream pig.
The method and manner in which pigs are passed through piping systems depend on the particular launching device that is used. Several U.S. Patents disclose pig launching devices, including U.S. Pat. No. 4,709,719 issued to Littleton et al, U.S. Pat. No. 3,562,014 issued to Childers et al, U.S. Pat. No. 3,322,140 issued to Scott and U.S. Pat. No. 5,139,576 issued to Davis.
Childers et al (U.S. Pat. No. 3,562,014) disclose a launching system for a pig scraper. In this system, the manipulation of valves and the application of fluid pressure launches the pig scrapers from a magazine connected to the production pipeline of interest.
Davis, in U.S. Pat. No. 5,139,576, and Scott, in U.S. Pat. No. 3,322,140, disclose pig launching systems in which pistons are used to launch pigs into horizontal gas transmission pipelines and pressurized pipelines, respectively. Davis discloses positioning a plurality of cup pigs within a horizontal storage magazine and using a piston to drive them into a downstream pipeline. The piston is driven by a liquid such as methanol.
In U.S. Pat. No. 3,322,140, Scott discloses a launcher for continuously injecting solid and semi-solid capsules into pressurized pipelines. The launcher includes a circulating loop having a conduit communicating between the pressurized pipeline and the loop. A launching ram communicates with a low pressure portion of the loop and is operable to introduce capsules into the loop, where they are carried to a high pressure portion of the loop and discharged into the pipeline.
Gravity is used in the pig launching and retrieval system disclosed in U.S. Pat. No. 4,709,719, issued to Littleton et al. In this system, a vertically oriented launching barrel is loaded with a number of cup pigs and placed in communication with the pipeline. The barrel contains a ram for launching cup pigs into the pipeline.
In addition to passing pigs through piping systems for cleaning and the like, launching systems are used to pass inspection or repair devices through piping systems in order to determine, from the piping interior, the location of cracks or other flaws in the piping. Such a launcher is known to be in use by VETCO Piping Services, Inc. of Houston, Tex. Normally, inspection devices or "rabbits" are pushed or pulled through piping systems with thick, sturdy cables. In this manner, negotiating bends in the piping systems is difficult because of the friction of the cable against the piping bends.
Using air pressure to send and receive documents in capsules through piping systems is also well known. There may be a sending pipe and a receiving pipe or there may be one pipe between source and destination and a valve to switch the direction of the air. However, these devices use a pipe dedicated to the movement of the capsule from one end of the piping system to the other and back and do not attempt to control the position or note the location of the capsule in the pipe.
Despite the abundance of cleaning pigs and inspection rabbits available for use in piping systems, there is a need for an improved inspection rabbit that does not rely on burdensome cables to maneuver the rabbit through the piping, especially around bends. Furthermore, the ability to control the direction of the pig or rabbit in the piping system is needed.